Posted
by
samzenpus
on Thursday February 07, 2013 @09:24PM
from the back-in-the-day dept.

sciencehabit writes "The ancestor of all placental mammals—the diverse lineage that includes almost all species of mammals living today, including humans—was a tiny, furry-tailed creature that evolved shortly after the dinosaurs disappeared, a new study suggests. The hypothetical creature, not found in the fossil record but inferred from it, probably was a tree-climbing, insect-eating mammal that weighed between 6 and 245 grams—somewhere between a small shrew and a mid-sized rat. It was furry, had a long tail, gave birth to a single young, and had a complex brain with a large lobe for interpreting smells and a corpus callosum, the bundle of nerve fibers that connects the left and right hemispheres of the brain. The period following the dinosaur die-offs could be considered a 'big bang' of mammalian diversification, with species representing as many as 10 major groups of placentals appearing within a 200,000-year interval."

The characteristics of the first placental are not really controversial. The real news here is that a lot of the work on placentals and eutherians is wrong and must be re-evaluated. Granted, a lot of the placental work was already merely tentative. Molecular phylogenetics estimates had placentals appearing about 105 Mya, This new work ignores the molecular results and comes up with a later date. From what I can see, dating of the relevant available fossils is equivocal.

Also curious is that according to this interpretation, the ancestral afrotherian (elephants, aardvarks, manatees, etc.) originated in South America and somehow migrated across the then 1000-mile ocean to Africa. Prepare for further revision.